1. Field of the Invention
This invention relates generally to the field of additive pumps that inject a chemical additive such as a dye, de-icing agent, detergent or the like into a liquid flow stream and specifically to a method and apparatus for powering an additive metering pump from the pressure head of said liquid flow stream and controlling it for proportionality.
2. Description of the Prior Art
A popular means of injecting chemical additives into various liquid streams, particularly fuels, is to use a signal generated from a flow meter in the recipient line to control a chemical injection pump. Most flow meters used for this purpose generate a discrete pulse as a given volume of fluid has flowed through the meter as opposed to providing a continuous signal whose amplitude is proportional to flow at a given instant. That is, each pulse from the product meter represents a fixed amount of product passing through the system. The pulse rate is used to pace various types of injection pumps capable of delivering the appropriate amount of additive for each pulse at sufficient pressure. This method is called pulse triggering.
The market contains many electric-powered metering pumps capable of pulse triggering from an external flow meter. However, for use with flammable fuels and around potentially explosive atmospheres, the injection system often uses a pneumatically-powered injection pump. Such a system is described in U.S. Pat. No. 4,370,996 to Williams. The use of compressed air may be disadvantageous because the air may contain moisture which is subject to freezing in cold climates. In addition, air operated components require some degree of lubrication in order to operate dependably.
Another alternative is to use a hydraulically-powered metering pump with control system such as disclosed in U.S. Pat. No. 6,135,719 to Yoder et al. This method has inherent overhead in requiring a dedicated hydraulic fluid system with head tank, pump, piping and associated components.
It is advantageous to use the solvent fluid to which the additive is to be injected as the hydraulic power for the injection pump, because it eliminates the overhead and complexity of an independent powering hydraulic system. This concept is commonly embodied in the prior art as inline venturi injectors.
In another embodiment of solvent fluid-powered injection systems, U.S. Pat. No. 4,119,113 to Meginniss teaches using a master-slave piston pump, wherein the master or driving piston is actuated by the solvent fluid flow and drives the slave or injection piston to add the chemical to the solvent flow downstream of the master piston. The '113 system is designed so that all of the solvent flow must pass through the master piston for metering purposes, limiting the maximum solvent flow rate and subjecting solvent flow to significant pressure drops and oscillations. Further, the system is confined to a fixed ratio dependant on the geometric design and arrangement of the master-slave piston pump. Because the injection ration is geometrically fixed, it is not easily adaptable for a variety of systems.
3. Identification of Objects of the Invention
A primary object of the invention is to provide a positive-displacement proportional chemical injection system, wherein the additive pump is powered by a pressure differential in the solvent line.
Another object of the invention is to provide a positive-displacement proportional chemical injection system having a widely adjustable mixing ratio.
Another object of the invention is to provide a positive-displacement proportional chemical injection system having a simplified open loop control based on solvent flow.
Another object of the invention is to provide a positive-displacement proportional chemical injection system having an injection pump immersed in the chemical additive to minimize introduction of air into the system.
Another object of the invention is to provide a positive-displacement proportional chemical injection system wherein the ratio adjustment is easily made by a user of the system.